Self-energized disc brake parking brake integral with a non-energized service disc brake

ABSTRACT

A disc brake assembly which contains a self-energized parking brake and a non-energized service brake. The service brake is actuated hydraulically, with fluid pressure acting on an inboard shoe peripheral section through the piston. An inboard shoe central section fitting within an opening of the shoe peripheral section is actuated mechanically through a self-energizing mechanism to provide parking brake capability. The two shoe sections have an overlapping construction such that movement of the peripheral section into braking engagement with the disc is transmitted to the shoe central section to also engage it with the disc. However, during the parking brake mode of operation only the central section engages the disc in braking relation. The brake mechanism is automatically adjusted as the brake shoes wear.

United States Patent 11 1 Warwick SELF-ENERGIZED DISC BRAKE PARKING Apr.2, 1974 BRAKE INTEGRAL WITH A Primary lz'xaminer(]eorge E. A. HalvosaNOMENERGMED SERWCE [)[SC BRAKE Assistant lfxaminerCharles E. Frankfort[75] Inventor: Edward H. Warwick, Englewood, Attorney Agent or McGraw 57ABSTRACT [73] Asslgncc: Ge'neraI Motm's Corp-t Dem), A disc brakeassembly which contains a self-encrgized parking brake and anon-energized service brake. The 22 Filed; APR 27, 1973 service brake isactuated hydraulically, with fluid pressure acting on an inboard shoeperipheral section PP Flo-13551189 through the piston. An inboard shoecentral section fitting within an opening of the shoe peripheral section52 us. 01. 188/106 F, 188/719, 188/73.l, is actuated mechanicallythrough Self-energizing 1 188/250 B mechanism to provide parking brakecapability. The 51 1m. 01. Fl6d 65/14, Fl6d 55/46 Shoe Sections have anoverlapping Construction [58] Field 61 Search 188/106 F, 72.6, 73.1,Such t movement of the Peripheral Section 188/722, 719 250 192/83, 107R, 85 AA braking engagement with the disc is transmitted to the l shoecentral section to also engage it with the disc. 56] References CitedHowever, during the parking brake mode of operation UNITED STATESPATENTS only the central section engages the disc in braking relation.The brake mechanism is automatically adjusted 3,456,765 7/1969 Meier188/726 as the brake shoes wfiar 3,422,933 H1969 VanHouse et al...l88/72,2, I r 3,047,098 7/1962 Olley l88/72.6 4 Claims, 2 DrawingFigures as I 2 a 20 v P662 If; as as 56 52 i 58 21 1 I 44 {9 K 'T' 1 K 1i159 awn I38 1 50 1 5 .118 Iw -LiC l v 8 an w I26 7 13s "I V l% 2 l w 1i a, 4:

SELF-ENERGIZED DISC BRAKE PARKING BRAKE INTEGRAL WITH A NON-ENERGIZEDSERVICE DISC BRAKE The invention relates to an automotive disc brakeunit having both service brake and parking brake capability. The servicebrake mode is accomplished through hydraulic pressure, and the parkingbrake mode is accomplished through mechanical actuation. The structurefor mechanically actuating the brake includes a self-energizingmechanism of the ball and ramp type. When the unit functions as ahydraulic disc brake, fluid pressure acts on a piston and the caliperhousing to force the piston against a peripheral portion of a brake padassembly. The peripheral brake pad assembly portion is so constructed inrelation to the central portion of the brake pad assembly that theperipheral portion also moves the central portion against one side ofthe disc. The pressure reaction on the caliper housing causesthe housingto slide in its mounting bracket so as to move the outboard brake padassembly'against the disc. The piston is annular in form and is locatedin an annular cylinder, with the mechanical brake actuating mechanismextending through the cylinder annulus.

lN THEDRAWING:

HO. 1 is a cross-section view, with parts broken away, of a disc brakeassembly embodying the invennon.

FIG. 2 is a view taken in the direction of arrows 22 of FIG. 1 andpresenting an elevation view of the inboard brake pad assembly of FIG.1.

The disc brake assembly is illustrated as being of the sliding calipertype similar to those currently in production use on many passengervehicles in. the United States. The assembly includes a disc 12 to bebraked, the disc having opposed friction surfaces 14 and 16. In thetypical installation in a vehicle, the disc 12 .is secured to arotatable wheel: so that the disc rotates with the wheel. The caliperassembly 18 includes caliper housing 20 formed to provide an outboardleg 22 and an inboard leg 24 joined. by a bridging section 26. The

The caliper housing inboard leg 24 is formed to provide a cylinderhousing 34 containing cylinder 36. The cylinder is open at the end.facing the disc 12 and is closed at its other end by a portion of thecylinder housing forming cylinder end wall 38. A sleeve 40 is secured tothe cylinder end wall 38 in a suitable manner, such as by the use ofrolling or staking, or the provision of a snap ring. The sleeve 40 isprovided with an end seal 42 which seals against the cylinder end wall38. It also has a seal 44- on its outer peripheral surface which issubstantially aligned in a concentric manner with seal 46 of cylinder36. Since sleeve 40 is spaced concentrically within cylinder 36, thecylinder and sleeve and end wall define an annular hydraulic pressurechamber 48. The provision of a small flange area on sleeve 40, whichcontains seal 42, with exposure to chamber 48, provides an area acted onby hydraulic pressure during hydraulic brake application which generatesa force urging sleeve 40 against end wall 38 for a tight seal. Anannular piston 50 is reciprocably received in the chamberformed bycylinder 36 and sleeve 40 so that the piston end wall 52 closes thepressure chamber 48.

Piston 50 extends outwardly of cylinder 36 toward disc 12 andterminatesin an annular end wall 54. Intermediate the piston end walls52 and 54 is a shoulder 56 formed on the piston so that the portion ofthe piston between shoulder 56 and end wall 54 has a larger innerdiameter than does the portion of piston 50 between shoulder 56 and endwall 52. The outer surface of piston 50 has a boot 58 mounted on thepiston and also on the enlarged portion of the cylinder housing at theopen end of cylinder 36 to protect the cylinder and piston from foreignmaterial.

The inner brake pad assembly 60, which is mounted on the caliper housingaxially intermediate piston end wall 54 and disc 12, is constructed witha peripheral section 62 and a central section 64. Section 62 includesthe peripheral shoe section 66 and peripheral lining section 68. Thecentral brake pad assembly section 64 includes the central shoe section70 and the central lining section 72. The peripheral shoe section 66 hasan opening 74 which is non-circular so that the central shoe sectionreceived therein cannot rotate within the opening. Opening 74 is definedby radially inner and outer edges 76 and 78 and circumferentially spacededges 80 and 82. Edges 80 and 82 are formed to provide shoulders 84 and86, respectively, and they are respectively provided with lips- 88 and90 which extend slightly inwardly of the opening relative to shoulders84 and 86. The peripheral lining section 68 is secured to the side ofperipheral shoe section 66 adjacent shoulders 84 and 86, and therefore,lips 88 and 90 are on the side of the shoe section facing piston 50. Thepiston end wall 54 is in abutting engagement with that side of theperipheral shoe section 66, and surrounds the opening 74.

I The shoe central section 70 is shaped much like opening 74 and hasradially inner and outer edges 92 and 94 which respectively mate withopening edges 76 and 78 in such a manner that the central shoe sectionis guided while being permitted to move slightly in directions generallycircumferential or tangential to the disc 12. The circumferentiallyspaced edges 96 and 98 of the shoe central section 70 respectivelycooperate with opening edges 80 and 82. The central shoe section edges96 and 98 are respectively formed to provide shoulders 100 and 102 andlips 104 and 106. Lips 88 and 104 overlap, as do lips 90 and 106, sothat lip 104 is aligned to abut shoulder 84' in brake force transmittingrelation as are lip 88 and shoulder 100, lip 90 and shoulder 92, and lip106 and shoulder 86. However, the lips and shoulders arecircumferentially spaced apart from this abutting relationship by adistance indicated by arrows 108 when the brake assembly is in thereleased position. As will be further described in the operation of thebrake, this distance is taken up by circumferential movement of thebrake pad assembly central section when the brake is mechanicallyactuated in the parking brake mode.

The inboard side of central shoe section 70 extends axially towardcylinder housing 34 and cooperates with a portion of piston 50 adjacentpiston end wall 54 to mount a boot 110 which seals the interior ofpiston 50 from the entry of foreign material. This side of the shoesection 70 is also provided with ramps 112 located radially within theaxially extending portion of the shoe section. These ramps are a part ofa ball and ramp mechanism 114 which will be further described.

The mechanical brake actuating mechanism 116 in cludes a screwshaft 118rotatably mounted in an aperture 120 formed in cylinder end wall 38substantially on the same axis as that of cylinder 36. Screw shaft 118has an actuating lever 122 secured to its outer end by a nut 124. Thelever is suitably connected so as to be moved arcuately, therebyrotating shaft 118, by a parking brake arrangement such as a parkingbrake cable connected to be tensioned by a suitable pedal or leverarrangement accessible for operation by the vehicle operator. Awasher-type spacer 126 may be provided between lever 122 and end wall138. Shaft 118 has a thrust flange 128 engaging a thrust washer 130 onthe inner side of end wall 38 which is capable of transmitting anythrust forcefrom flange 128 to the cylinder end wall. The inner end 132of shaft 118 is threaded with suitable screw threads 134 having a highlead. The threadedportion of shaft 118 extends through sleeve 40 towardthe central shoe section 70 of the brake pad assembly 60. An adjusternut 136 is internally threaded with screw threads 138 mating with screwthreads 134. Nut 136 has a generally cylindrical body 140 terminating ina flange 142 at the end thereof nearest the brake pad assembly 60. Anouter surface of the flange provides a clutch surface 144 of a clutch146. An adjuster cone 148, mounted axially intermediate the adjuster nut136 and the central shoe section 70, has an end wall 150 and an axiallyextending peripheral flange 152. This flange fits over the adjuster nut136 and has a clutch surface 154 formed therein in mating relation withclutch surface 144 and forming a part of clutch 146. The annular end 156of cone flange 152 is in axially spaced alignment with piston shoulder56, the normal spacing with the brake released being indicated by arrows158. Cone flange 152 also has secured to it a spring retainer 160, whichis generally hat shaped and extends within cylinder sleeve 40. Retainer160 is so formed to provide a seat 162 for compression spring 164, whichis positioned about the adjuster nut body 140. The other end of spring164 seats on a spring seat and thrust washer 166 which abuts against oneside of adjuster nut flange 142. The preload of spring 164 continuallyurges clutch surfaces 144 and 154 toward clutching engagement.

The'end wall 150 of cone 148 has ramps 168 formed therein and alsoproviding apart of the ball and ramp mechanism 114. Balls 170 arereceived by the ramps 112 and 168 and complete the ball and rampmechanism.

When the assembly functions as a service brake, it is hydraulicallyactuated. Fluid pressure is introduced into'chamber 48 and this pressureacts on piston and the cylinder end wall 38. The pressure forces thepiston leftwardly as seen in FIG. 1 against the peripheral shoe section66 so as to force the peripheral lining section 68 into brakingengagement with surface 16 of disc 12. Since lips 88 and 90 of theperipheral shoe section overlap lips 104 and 106 of thecentral shoesection, any force exerted on the peripheral shoe section in the brakeapply direction is also transmitted to the central shoe section.Therefore, the central lining section 72 is also moved into brakingengagement with the disc surface 16. The pressure in chamber 48 actingon the cylinder end wall 38 causes-the caliper housing to moverightwardly as seen in FIG. 1, sliding on pins 30, so as to move theoutboard brake pad assembly 172 into braking engagement with the surface14 of disc 12. The brake torque forces are transmitted from the brakepad assemblies 60 and 172 to the caliper housing bridging section 26,which in turn transmits these forces to a fixed portion of the brakeassembly. This type of arrangement is disclosed in U.S. Pat. No.3,628,639, entitled Disc Brake Caliper Mounting Means." The sleeve 40 issubjected to a small pressure differential across the annular areaindicated by arrows 174 which urges the sleeve more tightly into sealingengagement with the cylinder end wall 38 and assists in holding thesleeve in position.

When the central lining section 72 of brake pad assembly 60 engages discsurface 16 in braking relation, it moves circumferentially in thedirection of disc rotation, subject to the guiding action of openingedges 76 and 78. Assuming the disc to be rotating in the direction ofarrow 176, the central brake pad assembly 64 moves to close the spaceindicated by arrows 108 so that the brake torque is transmitted byshoulder and lip 104 to lip 88 and shoulder 84. The clearance so takenup is sufficiently limited to permit this movement of the central padassembly section 64 during hydraulic brake application without stoppingthe central brake pad assembly against the balls 170. Therefore,hydraulic brake applications are not self-energized. The spacingindicated by arrows 158 allows some apply movement of piston 50 withouthaving the shoulder 56 of the piston engaging the end 156 of cone 148,thus making an allowance for caliper housing deflection withouttransmitting brake apply force through the ball and ramp assembly 114.

The parking brake mode of operation is accomplished by moving the lever122 arcuately, thus rotating screw shaft 118. The force so transmittedalso tries to rotate the adjuster nut 136, but the nut is held againstrotation by the cone clutch mechanism since clutch 146 is engaged underforce of spring 164. Therefore, the force tries to rotate cone 148.However, the cone is prevented from'rotation by the balls 170 in theramps 112 and 168. The forces, therefore, try to rotate the central shoesection 70. This shoe section cannot rotate however, since it isreceived in a non-circular opening in the peripheral shoe section 66.The peripheral shoe section is prevented from rotation due to its torquetransmitting connection with the caliper housing bridging section, bestshown in FIG. 2. Therefore, on parking brake apply, the adjuster nut 136must advance as the screw shaft 1 18 is rotated and the brake applyforce acting axially due to this advance is transmitted.

through the clutch'146, the cone 148, and the ball and ramp mechanism114 to the central shoe section 70. As the central shoe section engagesthe disc, it moves so as to reduce the clearance indicated by arrows108, causing energization of the ball and ramp mechanism 1 14. Thereaction back through the mechanism is taken by the thrust washer whichapplies the outboard brake pad assembly 172 in' the same manner as onhydraulic applications.

The space indicated by arrows 158 is approximately equal to the maximumhousing deflection occurring in service braking. As the brake liningswear, this space is reduced and clearance develops across the ballswhich must be taken up on parking brake apply. Eventually a hydraulicapply operation takes place in which the housing deflection exceeds theremaining space 158. The shoulder 56 of piston 50 then contacts the coneend 156, moving the cone toward the disc relative to the adjuster nutand disengaging clutch 146. The adjuster spring 164, acting through thelow friction washer 166, causes the nut 136 to turn and advance on thescrew shaft 118 until the clutch is once again engaged. When thehydraulic pressure is then released, clearance develops at 158 which isequal to the amount of caliper deflection from that brake apply Thedifference between the original clearance at 158 and the resultingclearance is now the clearance across the balls 170. This allows forexpansion of the central section lining 72 with temperature withoutdragging the lining on the disc. Any expansion of the peripheral sectionlining 68 merely pushes the piston 50 backwardly into cylinder 36.

The disc brake assembly embodying the invention retains the desirablenon-energization effect of conventional disc brakes during hydraulicservice brake actuation. It has the advantageous characteristic thatless parking brake lever apply force is required since the parking brakeis self-energized through the ball and ramp mechanism 114. If desired,the central section lining 72 can be ofa different material with ahigher coefficient of friction than the peripheral section lining 68,thereby further reducing the input parking brake apply force required.Any tendency of the cone clutch 146 to slip or wedge, depending upon thecone angle, is prevented in this construction. The cone angle is biasedin the direction to wedge since the piston 50 will always be able torelease the clutch under influence of brake apply pressure. Thiseliminates the possibility of cone slippage during mechanical brakeapplications.

What is claimed is: v

1. A disc brake assembly comprising in combination:

a disc to be braked against rotation;

a caliper assembly having a first brake pad assembly and a second brakepad assembly mounted thereon and movable to engage said disc in frictionbraking relation, one of said brake pad assemblies having a peripheralsection and a central section mounted in and guided by and transmittingbraking force to said peripheral section and including means fortransmitting actuating forces from said peripheral section to saidcenter section;

first brake actuatingvmeans for actuating said one brake pad assemblyperipheral section and thereby actuating said one brake pad centralsection and by reaction actuating the other of said brake padassemblies;

and second brake actuating means actuable independently of said firstbrake actuating means for actuating said one brake pad assembly centralsection and by reaction actuating the other of said brake pad assembliesand including self-energizing means for generating a self-energizingforce that is effective only upon actuation of said second brakeactuating means.

2. A disc brake comprising;

a disc to be braked against rotation;

a caliper assembly including:

a caliper housing slidably mounted relative to said disc and having legsdisposed on opposite sides of said disc and a bridging section joiningsaid legs,

a cylinder formed in one of said caliper legs and having a brakeactuating piston reciprocably received therein,

a first .brake pad assembly mounted on said caliper housing axiallyintermediate the other of said caliper legs and said disc for frictionbraking engagement with said disc,

a second brake pad assembly mounted on said caliper housing axiallyintermediate said one caliper leg and said disc for frictionbrakingengagement with said disc,

said second brake pad assembly including a peripheral shoe having anon-circular opening therein and a peripheral lining secured thereto,

a non-circular central shoe received in said noncircular opening andhaving a central lining secured thereto,

said central and peripheral shoes having overlapping lipped shoulders atthe circumferentially spaced ends of said central shoe and providingspaced abutments for transmission of braking force from said centralshoe to said peripheral shoe upon relative movement thereof in acircumferential direction to abut the cooperating pairs of saidshoulders said peripheral lipped shoulders overlapping said central shoelipped shoulders axially on the side thereof away from said disc, saidperipheral shoe being engaged by said piston for braking actuation ofsaid peripheral and central shoes and linings;

and a manual brake actuator received in said caliper housing andincluding a threaded rotatable shaft having an adjuster nut thereon, aclutch formed by a clutch cone and a face on said adjuster nut, a balland ramp assembly having one ramp means formed in said clutch cone andthe other ramp means formed in said central shoe, and means urging saidclutch into engagement;

actuation of said manual brake actuator by rotation of said shaft actingthrough said nut and cone and ball and ramp assembly moving said centralshoe axially to engage the lining thereof with said disc, the rotationalmovement of said disc moving said central shoe in a circumferentialdirection to energize said ball and ramp assembly to self-energize saidbrake, and reaction force being exerted from said shaft to said caliperhousing to cause said first brake pad assembly to engage said disc inbraking relation.

3. A disc brake actuator comprising:

a caliper housing having a cylinder formed therein;

an annular sleeve secured in said cylinder to define therewith anannular pressure chamber for hydraulic brake actuation;

an annular piston reciprocably received in said cylinder and having oneend forming one wall of said annular pressure chamber and the other endengaging a disc brake pad assembly peripheral section and having aninwardly extending shoulder thereon axially interrnediate said pistonends and facing toward said disc brake pad assembly peripheral section;

a mechanical brake actuating mechanism including a rotatable input shaftrotatably mounted in said housing in thrust bearing relation thereto andextending through said sleeve and having threads on the inner endthereof, a threaded adjuster nut mounted on said threaded shaft innerend within said annular piston and said annular sleeve and having aclutch surface formed on one end thereof axially inward of said annularsleeve, an adjuster cone received within said annular piston axiallyadjacent said piston other end and having a clutch surface formed on aninner surface thereof and cooperating with said adjuster nut clutchsurface to provide a clutch, a spring retainer mounted on said cone anda compression spring acting on said retainer andsaid adjuster nut tourge said clutch into engagement, aself-energizing ball and ramp unithaving a set of balls and opposed sets of ramps receiving said balls,one set of ramps formed in the end of said cone opposite said adjusternut and the other set of ramps formed on a disc brake pad assemblycentral section mounted in said disc brake pad assembly peripheralsection for limited movement relative to said disc brake pad assemblyperipheral section and for brake torque force transmission thereto;

- said cone having another end facing said annular piston shoulder andwith the actuator released spaced therefrom by a distance substantiallyequal to caliper housing deflection with the actuator hydraulicallyactuated;

and the limited movement permitted in a disc circumferential directionbetween said disc brake pad assembly sections being less than themovement required to stop said disc brake pad assembly central sectionramp set against said balls when the actuator is hydraulically actuated.

4. In a disc brake having a caliper housing and a hydraulic brakeactuator and a mechanical brake actuator,

a disc brake pad assembly comprising: a first peripheral shoe sectionmovable in a brake apply direction by one of said brake actuators and 8formed with an opening therethrough defined by edges including two edgesspaced circumferentially relative to the disc to be braked and formedwith shoulders and lips extending over said shoulders providing brakeforce receiving surfaces, and brake lining secured to said shoe sectionon the side thereof adjacent said shoulders and opposite said lips; v asecond central shoe section movable in a brake apply direction by theother of said actuators and mating with and received in said first shoesection opening and having two edges spaced circumferentially relativeto the disc to be braked and formed with shoulders and lips extendingover said shoulders providing brake force transmitting surfaces, andbrake lining secured to said second shoe section on the side thereofadjacent said lips and opposite said shoulders; the shoulders and lipsof said first and second shoe section overlapping while permittinglimited movement of said second shoe section relative to said first shoesection in circumferential directions relative to the disc to be braked,the shoulders of said first shoe section and the lips of said secondshoe section and the lips of said first shoe section and the shouldersof said second shoe section being aligned so as to transmit and receivetherebetween brake force from said second shoe section to said firstshoe section upon movement of said second shoe section to engage an edgethereof with an edge of said first shoe section in brake forcetransmitting relation, said lips of said shoe sections also transmittingbrake apply force from said first shoe section to said second shoesection when said first shoe section is moved in the brake applydirection by one of the brake actuators.

1. A disc brake assembly comprising in combination: a disc to be brakedagainst rotation; a caliper assembly having a first brake pad assemblyand a second brake pad assembly mounted thereon and movable to engagesaid disc in friction braking relation, one of said brake pad assemblieshaving a peripheral section and a central section mounted in and guidedby and transmitting braking force to said peripheral section andincluding means for transmitting actuating forces from said peripheralsection to said center section; first brake actuating means foractuating said one brake pad assembly peripheral section and therebyactuating said one brake pad central section and by reaction actuatingthe other of said brake pad assemblies; and second brake actuating meansactuable independently of said first brake actuating means for actuatingsaid one brake pad assembly central section and by reaction actuatingthe other of said brake pad assemblies and including self-energizingmeans for generating a self-energizing force that is effective only uponactuation of said second brake actuating means.
 2. A disc brakecomprising: a disc to be braked against rotation; a caliper assemblyincluding: a caliper housing slidably mounted relative to said disc andhaving legs disposed on opposite sides of said disc and a bridgingsection joining said legs, a cylinder formed in one of said caliper legsand having a brake actuating piston reciprocably received therein, afirst brake pad assembly mounted on said caliper housing axiallyintermediate the other of said caliper legs and said disc for frictionbraking engagement with said disc, a second brake pad assembly mountedon said caliper housing axially intermediate said one caliper leg andsaid disc for friction braking engagement with said disc, said secondbrake pad assembly including a peripheral shoe having a non-circularopening therein and a peripheral lining secured thereto, a non-circularcentral shoe received in said non-circular opening and having a centrallining secured thereto, said central and peripheral shoes havingoverlapping lipped shoulders at the circumferentially spaced ends ofsaid central shoe and providing spaced abutments for transmission ofbraking force from said central shoe to said peripheral shoe uponrelative movement thereof in a circumferential direction to abut thecooperating pairs of said shoulders said peripheral lipped shouldersoverlapping said central shoe lipped shoulders axially on the sidethereof away from said disc, said peripheral shoe being engaged by saidpiston for braking actuation of said peripheral and central shoes andlinings; and a manual brake actuator received in said caliper housingand including a threaded rotatable shaft having an adjuster nut thereon,a clutch formed by a clutch cone and a face on said adjuster nut, a balland ramp assembly having One ramp means formed in said clutch cone andthe other ramp means formed in said central shoe, and means urging saidclutch into engagement; actuation of said manual brake actuator byrotation of said shaft acting through said nut and cone and ball andramp assembly moving said central shoe axially to engage the liningthereof with said disc, the rotational movement of said disc moving saidcentral shoe in a circumferential direction to energize said ball andramp assembly to self-energize said brake, and reaction force beingexerted from said shaft to said caliper housing to cause said firstbrake pad assembly to engage said disc in braking relation.
 3. A discbrake actuator comprising: a caliper housing having a cylinder formedtherein; an annular sleeve secured in said cylinder to define therewithan annular pressure chamber for hydraulic brake actuation; an annularpiston reciprocably received in said cylinder and having one end formingone wall of said annular pressure chamber and the other end engaging adisc brake pad assembly peripheral section and having an inwardlyextending shoulder thereon axially intermediate said piston ends andfacing toward said disc brake pad assembly peripheral section; amechanical brake actuating mechanism including a rotatable input shaftrotatably mounted in said housing in thrust bearing relation thereto andextending through said sleeve and having threads on the inner endthereof, a threaded adjuster nut mounted on said threaded shaft innerend within said annular piston and said annular sleeve and having aclutch surface formed on one end thereof axially inward of said annularsleeve, an adjuster cone received within said annular piston axiallyadjacent said piston other end and having a clutch surface formed on aninner surface thereof and cooperating with said adjuster nut clutchsurface to provide a clutch, a spring retainer mounted on said cone anda compression spring acting on said retainer and said adjuster nut tourge said clutch into engagement, a self-energizing ball and ramp unithaving a set of balls and opposed sets of ramps receiving said balls,one set of ramps formed in the end of said cone opposite said adjusternut and the other set of ramps formed on a disc brake pad assemblycentral section mounted in said disc brake pad assembly peripheralsection for limited movement relative to said disc brake pad assemblyperipheral section and for brake torque force transmission thereto; saidcone having another end facing said annular piston shoulder and with theactuator released spaced therefrom by a distance substantially equal tocaliper housing deflection with the actuator hydraulically actuated; andthe limited movement permitted in a disc circumferential directionbetween said disc brake pad assembly sections being less than themovement required to stop said disc brake pad assembly central sectionramp set against said balls when the actuator is hydraulically actuated.4. In a disc brake having a caliper housing and a hydraulic brakeactuator and a mechanical brake actuator, a disc brake pad assemblycomprising: a first peripheral shoe section movable in a brake applydirection by one of said brake actuators and formed with an openingtherethrough defined by edges including two edges spacedcircumferentially relative to the disc to be braked and formed withshoulders and lips extending over said shoulders providing brake forcereceiving surfaces, and brake lining secured to said shoe section on theside thereof adjacent said shoulders and opposite said lips; a secondcentral shoe section movable in a brake apply direction by the other ofsaid actuators and mating with and received in said first shoe sectionopening and having two edges spaced circumferentially relative to thedisc to be braked and formed with shoulders and lips extending over saidshoulders providing brake force transmitting surfaces, and brake liningsecured to said second shoe section on the Side thereof adjacent saidlips and opposite said shoulders; the shoulders and lips of said firstand second shoe section overlapping while permitting limited movement ofsaid second shoe section relative to said first shoe section incircumferential directions relative to the disc to be braked, theshoulders of said first shoe section and the lips of said second shoesection and the lips of said first shoe section and the shoulders ofsaid second shoe section being aligned so as to transmit and receivetherebetween brake force from said second shoe section to said firstshoe section upon movement of said second shoe section to engage an edgethereof with an edge of said first shoe section in brake forcetransmitting relation, said lips of said shoe sections also transmittingbrake apply force from said first shoe section to said second shoesection when said first shoe section is moved in the brake applydirection by one of the brake actuators.